Bacteriology Practice Questions

Q: Which of the following is true about H. pylori?

Produces Vacuolating cytotoxin. **Explanation:** *Helicobacter pylori* is a microaerophilic, Gram-negative spiral bacterium primarily associated with peptic ulcer disease and gastric carcinoma. **Why Option A is Correct:** *H. pylori* possesses several virulence factors, the most significant being the **Vacuolating cytotoxin (VacA)** and the **Cytotoxin-associated gene A (CagA)**. VacA induces the formation of large cytoplasmic vacuoles in gastric epithelial cells, leading to cell death and tissue damage. Strains expressing both VacA and CagA (Type I strains) are more strongly associated with severe inflammation and malignancy. **Why Other Options are Incorrect:** * **Option B:** While Type I strains are more virulent, **Anti-CagA antibodies** (not antiurease) are the specific markers used to identify these aggressive strains. Urease is produced by almost all *H. pylori* strains to neutralize gastric acid; therefore, antiurease antibodies lack specificity for Type I. * **Option C:** *H. pylori* specifically colonizes the **gastric mucosa** (primarily the antrum). It does not inhabit the jejunum, as it requires the specific pH environment and mucosal receptors found in the stomach. * **Option D:** Treatment involves **Triple Therapy** (Clarithromycin, Amoxicillin/Metronidazole, and a Proton Pump Inhibitor). Al(OH)₃ is an antacid used for symptomatic relief but has no curative or antimicrobial effect against the infection. **High-Yield Clinical Pearls for NEET-PG:** * **Urease Breath Test:** The non-invasive "Gold Standard" for monitoring treatment success. * **Biopsy Urease Test (RUT):** A rapid invasive test (color change from yellow to pink). * **MALToma:** *H. pylori* is a Class I carcinogen; its eradication can lead to the regression of low-grade gastric MALT lymphoma. * **Culture:** Uses Skirrow’s medium or Chocolate agar.

Q: True about V. Cholerae is:

Pathogenicity of O-139 Vibrio is due to O antigen.. ### Explanation **Correct Option: D. Pathogenicity of O-139 Vibrio is due to O antigen.** The pathogenicity of *Vibrio cholerae* O139 (Bengal strain) is unique because it possesses a specific **O-antigen polysaccharide** and a **capsule**, both of which are essential for its virulence. Unlike the O1 serogroup, O139 has a distinct lipopolysaccharide (LPS) structure that allows it to cause epidemic cholera even in populations with pre-existing immunity to O1. **Analysis of Incorrect Options:** * **Option A:** Immunity following a natural infection with *V. cholerae* is **not lifelong**. While it provides significant protection against the same serogroup for approximately 3–10 years (longer for El Tor than Classical), it does not last a lifetime. * **Options B & C:** In **endemic (non-epidemic) regions**, cholera primarily affects **children**. This is because adults in these areas have usually developed acquired immunity through repeated subclinical exposures. In contrast, in **epidemic/pandemic** situations (where the population is "immunologically naive"), both adults and children are affected with equal propensity. **High-Yield Clinical Pearls for NEET-PG:** * **Serogroups:** Only O1 and O139 cause epidemic cholera. O1 is further divided into biotypes (Classical and El Tor) and serotypes (Ogawa, Inaba, Hikojima). * **Mechanism:** Pathogenicity is primarily mediated by the **Cholera Toxin (Choleragen)**, which increases intracellular **cAMP**, leading to the hypersecretion of water and electrolytes (Rice-water stools). * **Culture:** **TCBS (Thiosulfate Citrate Bile Salts Sucrose)** agar is the selective medium of choice, where *V. cholerae* produces large yellow colonies due to sucrose fermentation. * **Transport Media:** Venkatraman-Ramakrishnan (VR) medium or Cary-Blair medium are used for stool samples.

Q: 'Bull neck' in Diphtheria is due to which of the following?

Lymphadenopathy. **Explanation:** The hallmark clinical feature of **Diphtheria** (caused by *Corynebacterium diphtheriae*) is the formation of a greyish-white pseudomembrane. The characteristic **'Bull neck' appearance** is primarily due to massive **cervical lymphadenopathy** and associated periadenitis (inflammation of the tissues surrounding the lymph nodes) and edema in the soft tissues of the neck. **Analysis of Options:** * **D. Lymphadenopathy (Correct):** The diphtheria toxin causes local tissue destruction and intense inflammation. This leads to significant enlargement of the cervical lymph nodes. When combined with surrounding soft tissue edema, it obliterates the angle of the jaw, resulting in the "Bull neck" deformity. * **A. Retropharyngeal abscess:** While this can cause neck swelling, it is typically a complication of pyogenic infections (like *S. aureus*) or TB (Pott’s spine), not the primary cause of the classic diphtheritic bull neck. * **B. Laryngeal edema:** This occurs in laryngeal diphtheria and leads to airway obstruction and stridor, but it does not manifest as external "bull neck" swelling. * **C. Cellulitis:** Although there is inflammation of the subcutaneous tissues (periadenitis), the primary pathological driver and clinical descriptor for this specific sign is the profound lymph node involvement. **High-Yield Clinical Pearls for NEET-PG:** * **Schick Test:** Used to demonstrate immunity/susceptibility to diphtheria. * **Culture Media:** Loeffler’s Serum Slope (rapid growth) and Potassium Tellurite agar (black colonies). * **Microscopy:** Gram-positive bacilli showing **Chinese letter pattern** (cuneiform) and **Volutin/Metachromatic granules** (Albert’s stain). * **Virulence:** Mediated by an exotoxin (fragment A inhibits Protein Synthesis via EF-2). * **Complications:** Myocarditis (most common cause of death) and neurological deficits (palatal paralysis).

Q: The Weil-Felix reaction with OXK antigen indicates infection with which of the following organisms?

Rickettsia tsutsugamushi. ### Explanation The **Weil-Felix reaction** is a heterophile agglutination test used for the presumptive diagnosis of Rickettsial diseases. It relies on the cross-reactivity between antibodies produced during certain rickettsial infections and the somatic (O) antigens of specific strains of **Proteus vulgaris (OX19, OX2)** and **Proteus mirabilis (OXK)**. **1. Why Option A is Correct:** * **Rickettsia tsutsugamushi** (now *Orientia tsutsugamushi*), the causative agent of **Scrub Typhus**, is the only major rickettsial pathogen that reacts specifically with the **OXK** antigen. It does not react with OX19 or OX2. **2. Why the Other Options are Incorrect:** * **Option B: Rickettsia mooseri** (now *R. typhi*) causes Endemic (Murine) Typhus. It shows a strongly positive reaction with **OX19** and a weak/negative reaction with OXK. * **Option C: Rickettsia quintana** (now *Bartonella quintana*) causes Trench Fever. It is **Weil-Felix negative**, as are most Bartonella species. * **Option D: Rickettsia akari** causes Rickettsialpox. Along with *R. prowazekii* (Epidemic typhus), it typically shows a negative Weil-Felix reaction (or very low titers), making the test unreliable for these specific infections. **High-Yield Clinical Pearls for NEET-PG:** * **Scrub Typhus (OXK+):** Transmitted by the bite of a **larval mite (chigger)**; characterized by a pathognomonic **black eschar**. * **Epidemic Typhus (OX19+):** Caused by *R. prowazekii*; transmitted by the **human body louse**. * **Rocky Mountain Spotted Fever (OX19+ and OX2+):** Caused by *R. rickettsii*; transmitted by ticks. * **Limitation:** The Weil-Felix test lacks high sensitivity and specificity; definitive diagnosis is now preferred via Indirect Immunofluorescence Assay (IFA) or PCR.

Q: How are diphtheria carriers diagnosed?

Throat culture. **Explanation:** The diagnosis of a **diphtheria carrier** (an individual who harbors *Corynebacterium diphtheriae* without clinical symptoms) relies on the isolation of the organism from the site of colonization, typically the throat or nose. **1. Why Throat Culture is Correct:** Culture is the gold standard for identifying carriers. Swabs are taken from the throat and nose and inoculated onto selective media like **Loeffler’s Serum Slope** (rapid growth) or **Potassium Tellurite Agar** (selective medium where colonies appear black). Since carriers do not have a visible pseudomembrane, culture is the only definitive way to detect the presence of the bacteria. **2. Why Other Options are Incorrect:** * **Gram’s Staining:** This is non-specific. Many commensal "diphtheroids" in the normal throat flora resemble *C. diphtheriae* morphologically, making it impossible to distinguish a carrier from a healthy individual via Gram stain. * **Albert’s Staining:** This is used to demonstrate **metachromatic granules** (Volutin/Babes-Ernst granules). While it helps in presumptive diagnosis of an active case, it cannot definitively confirm a carrier state because some non-pathogenic corynebacteria also possess these granules. * **Schick Test:** This is an obsolete skin test used to determine the **immune status** (susceptibility) of an individual to diphtheria toxin. It does not detect the presence of the bacteria itself. **NEET-PG High-Yield Pearls:** * **Elek’s Gel Precipitation Test:** Used to differentiate toxigenic strains from non-toxigenic strains (essential for confirming a "dangerous" carrier). * **Treatment for Carriers:** Oral **Erythromycin** is the drug of choice to eradicate the carrier state. * **Virulence Factor:** Diphtheria toxin acts by inhibiting **EF-2** (Elongation Factor-2), halting protein synthesis.

Q: Malignant pustules are characteristic of which type of infection?

Anthrax infection. **Explanation:** **Malignant pustule** is the characteristic clinical lesion of **Cutaneous Anthrax**, caused by *Bacillus anthracis*. Despite the name, it is neither malignant (cancerous) nor a true pustule (as it contains serosanguinous fluid rather than pus). 1. **Why Anthrax is correct:** In cutaneous anthrax, the spores enter through abraded skin. The lesion begins as a painless papule, progresses to a vesicle, and eventually undergoes central necrosis to form a **painless, depressed black eschar** surrounded by significant non-pitting edema. The term "malignant" historically referred to the severity of the untreated infection, which can lead to fatal septicemia. 2. **Why other options are incorrect:** * **Epithelioma & Melanoma:** These are neoplastic (cancerous) conditions. While "malignant" is a term used in oncology, these do not present as "pustules" or acute infectious eschars. Melanoma is a malignancy of melanocytes, and epithelioma refers to tumors of the epithelium. * **Tetanus:** Caused by *Clostridium tetani*, this is a toxemic disease characterized by muscular rigidity and spasms (lockjaw). It does not produce a localized skin lesion like a malignant pustule. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *Bacillus anthracis* (Gram-positive, spore-forming, non-motile "Bamboo-stick" appearance). * **Key Feature:** The eschar is characteristically **painless**, which helps differentiate it from pyogenic abscesses or Orf. * **Occupational Hazard:** Also known as **Hide-porter’s disease**, as it commonly affects those handling infected animal products (wool, hides). * **Virulence Factors:** Capsule (poly-D-glutamic acid) and Anthrax toxin (Edema factor, Lethal factor, and Protective antigen). * **McFadyean’s Reaction:** Used for presumptive identification of *B. anthracis* using polychrome methylene blue stain to visualize the capsule.

Q: Stalactite growth in a ghee broth culture is characteristic of which bacterium?

Yersinia. **Explanation** The correct answer is **Yersinia pestis**. **1. Why Yersinia is Correct:** *Yersinia pestis*, the causative agent of plague, exhibits a unique growth pattern in liquid media containing a layer of oil or fat. When grown in **Ghee broth** (clarified butter) or broth with oil, the bacteria grow as delicate, hanging filaments or "icicle-like" structures extending downwards from the surface. This is known as **Stalactite growth**. This occurs because the organism is non-motile and prefers the interface between the lipid and the broth for optimal growth. **2. Why Other Options are Incorrect:** * **Bacillus:** *Bacillus anthracis* typically shows a "Medusa head" appearance on agar plates and a "inverted fir tree" appearance in gelatin stabs, but not stalactite growth. * **Legionella:** This is a fastidious organism that requires buffered charcoal yeast extract (BCYE) agar supplemented with L-cysteine and iron. It does not show specific growth patterns in ghee broth. * **Leptospira:** These are spirochetes that require specialized media like EMJH (Ellinghausen-McCullough-Johnson-Harris). They are highly motile and do not form stalactites. **3. High-Yield Clinical Pearls for NEET-PG:** * **Safety Note:** *Y. pestis* is a Tier 1 Select Agent; laboratory diagnosis requires extreme caution (BSL-3). * **Microscopy:** Shows characteristic **"Safety-pin" appearance** (bipolar staining) with Wayson or Giemsa stain. * **Culture:** On blood agar, it forms "fried egg" colonies. * **Vector:** Transmitted by the rat flea (*Xenopsylla cheopis*). * **Virulence Factor:** F1 antigen (capsular) and V/W antigens.

Q: What is the most common sensitive causative organism for Traveller's diarrhoea?

E. coli. **Explanation:** **Traveller’s Diarrhoea (TD)** is defined as the passage of three or more unformed stools in a 24-hour period, often accompanied by abdominal cramps, nausea, or bloating, occurring in individuals traveling from developed to developing regions. **Why E. coli is correct:** The most common causative agent worldwide is **Enterotoxigenic *Escherichia coli* (ETEC)**. It accounts for approximately 30–50% of cases. ETEC colonizes the small intestine and produces two types of enterotoxins: **Heat-labile (LT)**, which increases cAMP, and **Heat-stable (ST)**, which increases cGMP. Both lead to the hypersecretion of water and electrolytes, resulting in watery diarrhea. **Analysis of Incorrect Options:** * **Shigella:** While a common cause of bacterial dysentery (bloody diarrhea), it is less frequent than ETEC in travelers. It typically presents with high fever and mucoid stools. * **Norwalk virus (Norovirus):** This is the leading cause of epidemic gastroenteritis and is frequently associated with **cruise ships** and institutional outbreaks, but it ranks behind ETEC for general traveler’s diarrhea. * **Rotavirus:** This is the most common cause of severe diarrhea in **infants and young children** globally, but it is not the primary cause of traveler's diarrhea in adults. **NEET-PG High-Yield Pearls:** * **Most common bacterial cause:** ETEC (Enterotoxigenic *E. coli*). * **Most common parasite:** *Giardia lamblia*. * **Drug of choice (Prophylaxis):** Fluoroquinolones (e.g., Ciprofloxacin) or Rifaximin. * **Mechanism of ETEC LT toxin:** Similar to Cholera toxin (ADP-ribosylation of Gs protein → ↑cAMP). * **Clinical Tip:** If the question specifies "bloody diarrhea in a traveler," consider *Campylobacter* or *Shigella*.

Question 1

Which of the following is true about H. pylori?

Accepted Answer

Produces Vacuolating cytotoxin

Answer

Antiurease antibody detection is specific for type I strains

Answer

Inhabits the jejunum

Answer

Treatment involves Al(OH)2

Question 2

True about V. Cholerae is:

Accepted Answer

Pathogenicity of O-139 Vibrio is due to O antigen.

Answer

One attack of V. Cholerae gives lifelong immunity.

Answer

Affects adults and children with equal propensity in non-epidemic regions.

Answer

Affects adults and children with equal propensity in non-epidemic regions.

Question 3

Which is not a typical mechanism of action of obligate anaerobes for producing energy?

Accepted Answer

Produce energy by exploiting the cytochrome system

Answer

Absence of air enhancing their growth potential

Answer

Lack of the enzyme catalase

Answer

Devoid of superoxide dismutase

Question 4

'Bull neck' in Diphtheria is due to which of the following?

Accepted Answer

Lymphadenopathy

Answer

Retropharyngeal abscess

Answer

Laryngeal edema

Answer

Cellulitis

Question 5

The Weil-Felix reaction with OXK antigen indicates infection with which of the following organisms?

Accepted Answer

Rickettsia tsutsugamushi

Answer

Rickettsia mooseri

Answer

Rickettsia quintana

Answer

Rickettsia akari

Question 6

Bilateral tonsillectomy is performed on an otherwise healthy 11-year-old female with recurrent upper respiratory tract infections. On pathological examination of the tonsils, numerous small, yellow granules are noted. A granule crushed between two slides reveals a dense, gram-positive center and numerous branching filaments at the periphery. The granules are most likely composed of which of the following organisms?

Accepted Answer

Actinomyces israelii

Answer

Aspergillus fumigatus

Answer

Blastomyces dermatitidis

Answer

Candida albicans

Question 7

How are diphtheria carriers diagnosed?

Accepted Answer

Throat culture

Answer

Gram's staining

Answer

Albert's staining

Answer

Schick test

Question 8

Malignant pustules are characteristic of which type of infection?

Accepted Answer

Anthrax infection

Answer

Epithelioma

Answer

Melanoma

Answer

Tetanus

Question 9

Stalactite growth in a ghee broth culture is characteristic of which bacterium?

Accepted Answer

Yersinia

Answer

Bacillus

Answer

Legionella

Answer

Leptospira

Question 10

What is the most common sensitive causative organism for Traveller's diarrhoea?

Accepted Answer

E. coli

Answer

Shigella

Answer

Norwalk virus

Answer

Rotavirus

Bacteriology — MCQs

Bacteriology — MCQs

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